The Dominators make their first appearance in this story by Jim Shooter and Curt Swan, though they are not the villains in Adventure 361 (Oct 67). Kandro Boltax also makes his real first appearance, having been impersonated in the previous two issues.
The Dominators are introduced as having been at war with the United Planets for 20 years, but currently negotiating a peace settlement. Kandro Boltax asks the Legion to escort them through an “under-dimension,” as anto-Domintor feelings are high, and there is information indicating that the delegates will be attacked by assassins known as the Unkillables.
Little is developed about the Dominators in this tale, and they only sightly resemble their later appearance. There is no element of the caste system, or differently sized discs on their heads.
The story is meant to be suspenseful – the Legionnaires wonder when and where they will be attacked, and whether they can trust the Dominators, but it never really picks up, at least in my eyes.
Ultimately, it turns out the entire mission was a ruse, as the Dominators they are accompanying are just three-dimensional illusions. The revelation that the Unkillables are clones of Brutus, Cassius, John Wilkes Booth and Lee Harvey Oswald doesn’t help the tale either. Finally, Jim Mooney’s inks all but obliterate Curt Swan’s pencils.
The Dominators do not return until the Earthwar saga in the 70s.